为什么不打印堆栈跟踪？

Question

While trying to print the stack trace in my browser window, I fail. Following is the sample of the exception block.

try {
    // Add Code Here
} catch(Exception exc) { exc.printStackTrace();}

I am using google app engine as my server. What could be the reason the stack trace is not printing ?

Answer 1

Because there is no Exception to catch:

try {
    // Add Code Here
}

You will only print a stack trace an Exception is thrown within the try block like this:

try {
    throw new RuntimeException();
}

Answer 2

The method in question is implemented like this:

public void printStackTrace() {
    printStackTrace(System.err);
}

If your container/IDE/framework redirects the stream then you will not observe it at the expected location, see also System.setErr(...); . And of course, I expect you to have checked that your code really throws an Exception (if an Error then it will not be caught by your clause).

Answer 3

You will need to change the default error output stream. Since you are most probably coding a servlet , you could change to :

exc.printStackTrace(response.getWriter());

This will print the exception trace into the browser window.